NATURAL PHILOSOPHY. 237 



his own dial, which, though large, was portable, with means of setting it in 

 the meridian and truly horizontally, which he explained. The circle of the 

 dial was about thirteen inches diameter; towards its south point a fine 

 needle rose, from which two human hairs proceeded, one in a fixed position, 

 parallel to the earth's axis at the place ; this was supported by a stout brass 

 arch, which could be shortened or lengthened, and which had a fine slit at its 

 upper part to hold the fixed hair. The shadow of this hair the author stated 

 was always sharp and well-defined for about three inches from the needle, 

 round which a small hour-circle of about that diameter was graduated. The 

 floating hair, as the author called it, being taken by the hand and laid along 

 the shadow of the fixed hair so as to bisect it where it was sharp, was 

 stretched out to an outer graduated hour-circle, where the induction could 

 be easily read off to a fraction of a minute, amounting to a few seconds. 



KEW TELESCOPE FOR THE PARIS OBSERVATORY. 



A new telescope of the largest dimensions is now in the process of con- 

 struction for the Paris Observatory. The objective of the telescope will be 

 constructed with two discs of flint glass and crown glass, cast in the glass- 

 house of Chauce & Co., Birmingham, England, which w r ere on exhibition at 

 the Crystal Palace in Paris. These glasses were imperfectly appreciated by 

 the jury ; for it was thought that after extracting certain portions that were 

 not perfectly transparent and remelting them several times, they would not 

 afford an objective over forty centimetres in diameter. They were, how- 

 ever, deemed irreproachable, and were purchased for 50,000 francs ; and it is 

 now expected that the objective made from them will leave a diameter of 

 seventy-three centimetres. If the curvature obtained be perfect, the achro- 

 matism without fault, and the expected size be attained, France will have 

 the most powerful lens in the world. 



TELESCOPE STEREOSCOPES. 



Mr. Jas. Elliot, in a communication to the Philosophical Magazine (Lon- 

 don, Jan. 1857), states that he has recently succeeded in constructing what 

 he believes to be a new form of the stereoscope. Its object is to unite large 

 binocular photographic pictures in a different way from any that has hitherto 

 been followed. The pictures are placed side by side, and viewed through 

 two small telescopes, like those of opera-glasses, with the directions of their 

 axes crossing each other ; the left hand picture being viewed with the right 

 eye, and the right-hand picture with the left eye. The two telescopes are 

 connected together, the connecting apparatus being capable of two adjust- 

 ments ; one to suit the width of the eyes, and the other to give the obliquity 

 required. When the instrument is placed on a stand, as I have it, two other 

 adjustments are required ; the first to bring the telescopes to the proper ele- 

 vation, and the second to bring the plane of then- axes into parallelism with 

 the upper or lower margins of the pictures. 



.The_jnstrumcnt is constructed in such a way that these adjustments are 



